Commercial and residential buildings and structures can include many building system components. In some cases, the building components may be gas-fired building components such as furnaces, boilers, water heaters, deep fryers, as well as many other types of gas-fired building components. Gas-fired building components often include a combustion system acting as the heating system for the component. One example combustion system may include a gas source, a gas valve to regulate the gas source, a burner, an ignition system to ignite the burner when desired, and a controller to control the operation of the combustion system.
In some combustion systems, a flame rod may be provided to sense the presence of the flame, indicating that the gas burner is ignited. In this case, the presence of the flame may be detected by an ionization current in the flame rod. To detect the ionization current, the controller may apply an alternating current voltage between the flame sensing rod and the base of the flame (i.e. ground). The ions in the flame may provide a high resistance current path between the flame rod and the ground. Because the surface of the flame base is larger than the flame rod, more electrons may flow in one direction than the other, resulting in a relatively small direct current (DC) offset current. When a flame is present, this DC offset may be detected by the controller, which may indicate that a flame is present. The controller may then control the operation of the combustion system according to the presence of the flame. For example, when the flame is present, the controller may further open and/or leave open the gas valve and/or air flow dampers. If there is no flame present the controller may close the gas valve or take other action.
In many cases, the drive signal for the flame rod may need to be a relatively high-voltage AC signal, such as 100 Volts, 200 Volts or the like. However, in many cases, the control system may only have a relatively low voltage power source available, such as 24 Volts, 5 Volts or the like. As such, the control system may need to boost the low voltage into a high voltage source to generate the flame sensing signal. In some cases, to boost the relatively low voltage source, a DCDC step-up circuit may be used. In this case, the DCDC step-up circuit may be able to generate a high voltage DC power source, which may then be chopped to generate the desired high-voltage AC signal for the flame rod. However, this method can add significant cost to the control system. Therefore, there is a need for alternative control systems that can generate a relatively high voltage AC signal to drive a flame rod.